Kenda Standard Inner Tube Features: Dependable inner tubes available in sizes to fit most models Butyl rubber for good air retention, carefully molded for uniformity and precision quality Long wear and piece of mind Tr-4 and Tr-6 metal center valve stem Tr-4 uses an oval-shaped transition from valve to the body of the inner tube Tr-6 uses a round interface Metal valve stem construction with lock nuts Note : Tr-4 and Tr-6 valve stem styles, and types can be used interchangeably.